(CNN) Colorado investigators say they found no incidents of criminal activity following an investigation into mysterious drone sightings over Colorado and Nebraska.
"In response to public concern over reports of unusually large-sized drones flying patterns in groups, (the Colorado Department of Public Safety) has been gathering and analyzing information since November 23 and has conducted field investigations since January 6," CDPS said in a news release.
But their investigations didn't substantiate the drone reports, the release said.
The department said Colorado officials had received 90 reports of drone activity between November 23 to January 23 and of those, 14 were confirmed to be hobbyist drones.
It also said that there were 23 drone reports since January 6 -- 13 of which were determined to be "planets, stars or small hobbyist drones," six were ruled out as atmospheric conditions or commercial aircraft and the last four couldn't be identified by law enforcement.
"Colorado has a significant presence of legal professional and hobby drone operators," according to the findings in the release. "Based on the data gathered and analyzed during these investigations, CDPS will scale back proactive operations but will continue to respond to and investigate reports of suspicious activity."
And while officials can't say they've quite solved the mystery, they've ruled out a lot of the activity causing concern, CDPS Executive Director Stan Hilkey said in a statement.
"We will continue to remain vigilant and respond as new information comes in," Hilkey added.
Earlier this month, a Colorado sheriff's office said they were meeting with local, state and federal authorities to get to the bottom of the issue and asked for the public's help in identifying a command vehicle.
"We are looking for a closed box trailer with antennas or a large van that does not belong in the area," the Phillips County Sheriff's Office in Holyoke, Colorado, had said.
Colorado Sen. Cory Gardner also became involved, saying he was closely monitoring the drone situation.
"I've been in contact with the FAA regarding the heavy drone activity in Eastern Colorado and I'm encouraged that they've opened a full investigation to learn the source and purpose of the drones," he had tweeted.